1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to blowout preventers and an opening chamber head that are configured to withstand deformations created by high pressures.
2. Discussion of the Background
During the past years, with the increase in price of fossil fuels, the interest in developing new production fields has dramatically increased. However, the availability of land-based production fields is limited. Thus, the industry has now extended drilling to offshore locations, which appear to hold a vast amount of fossil fuel.
The existing technologies for extracting the fossil fuel from offshore fields use a system 10 as shown in FIG. 1. More specifically, the system 10 includes a vessel 12 having a reel 14 that supplies power/communication cords 16 to a controller 18. A reel may be used to transmit power and communication. Some systems have hose reels to transmit fluid under pressure or hard pipe (rigid conduit) to transmit the fluid under pressure or both. Other systems may have a hose with communication or lines (pilot) to supply and operate functions subsea. However, a common feature of these systems is their limited operation depth. The controller 18, which will be discussed later, is disposed undersea, close to or on the seabed 20. In this respect, it is noted that the elements shown in the figures are not drawn to scale and no dimensions should be inferred from the figures.
FIG. 1 also shows a wellhead 22 of the subsea well and a production tubing 24 that enters the subsea well. At the end of the production tubing 24 there is a drill (not shown). Various mechanisms, also not shown, are employed to rotate the production tubing 24, and implicitly the drill, to extend the subsea well.
However, during normal drilling operation, unexpected events may occur that could damage the well and/or the equipment used for drilling. One such event is the uncontrolled flow of gas, oil or other well fluids from an underground formation into the well. Such event is sometimes referred to a “kick” or a “blowout” and may occur when formation pressure exceeds the pressure applied to it by the column of drilling fluid. This event is unforeseeable and if no measures are taken to prevent it, the well and/or the associated equipment may be damaged.
Another event that may damage the well and/or the associated equipment is a hurricane or an earthquake. Both of these natural phenomena may damage the integrity of the well and the associated equipment. For example, due to the high winds produced by a hurricane at the surface of the sea, the vessel or the rig that powers the undersea equipment starts to drift resulting in breaking the power/communication cords or other elements that connect the well to the vessel or rig. Other events that may damage the integrity of the well and/or associated equipment are possible as would be appreciated by those skilled in the art.
Thus, a blowout preventer (BOP), later to be expressed as BOP only, might be installed on top of the well to seal it in case that one of the above events is threatening the integrity of the well. The BOP is conventionally implemented as a valve to prevent the release of pressure either in the annular space between the casing and the drill pipe or in the open hole (i,e., hole with no drill pipe) during drilling or completion operations. FIG. 1 shows BOPs 26 or 28 that are controlled by the controller 18. The blowout preventer controller 18 controls an accumulator 30 to close or open BOPs 26 and 28. More specifically, the controller 18 controls a system of valves for opening and closing the BOPs. Hydraulic fluid, which is used to open and close the valves, is commonly pressurized by equipment on the surface. The pressurized fluid is stored in accumulators on the surface and subsea to operate the BOPs. The fluid stored subsea in accumulators may also be used to autoshear and/or for deadman functions when the control of the well is lost. The accumulator 30 may include containers (canisters) that store the hydraulic fluid under pressure and provide the necessary pressure to open and close the BOPs. The pressure from the accumulator 30 is carried by pipe or hose 32 to BOPs 26 and 28.
One type of BOP is the annular blowout preventer, an example of which is shown in FIG. 2. The annular BOP 26 has a body 40 in which is formed a cavity 42. The drill line (not shown) crosses through the cavity 42. The annular BOP 26 is attached to the well head 22 via a flange 44. A packer 46 is formed inside the cavity 42 of the body 40, around the drill line so that the packer 46 does not affect the movement of the drill line when the BOP is open. A static head 48 is attached to the body 40 to close the cavity 42 and also to prevent the packer 46 to exit the body 40. A piston 50 is provided in a recess of the body 40 to not affect the movement of the drill line through the cavity 42. The piston 50 is shown in FIG. 2 not pressing on the packer 46.
However, when piston 50 is actuated by the high pressure from the accumulator 30, the piston 50 moves towards the packer 46, squeezing the packer 46 such that a portion of the packer 46 presses against the drill line and seals the well. When the piston 50 moves upward, an opening chamber 52 decreases in size until an upper tip of piston 50 touches or is close to touch an opening chamber head 60. The closing pressure that actuates the piston 50 enters the closing chamber 58 (shown in FIG. 3) via an inlet 54. Once the piston 50 is closed, the high pressure from the closing chamber 58 is vented out so that the piston 50 is prepared for the opening phase. At this stage, it was observed that the piston 50 may move downwards, resulting in the occurrence of a low pressure or vacuum on a lower part A of the opening chamber head 60 while a high pressure (from sea water for example) may appear on an upper part B of the opening chamber head 60 as shown in FIG. 3.
FIG. 3 shows in more details the opening chamber head 60 being in contact with the static head 48, the piston 50 and the body 40. The opening chamber head 60 has a recess 62 in which o-rings are placed to seal the opening chamber 52. Due to the vacuum that occurs when the piston 50 moves backwards after the piston 50 was closed, it was observed that the opening chamber head 60 deforms due to the high pressure difference between sides A and B. As the opening chamber head 60 ensures that the hydraulic liquid in the opening chamber 52 remains free of contamination from outside, the deformation of the opening chamber head 60 is undesired as it reduces the time interval between scheduled maintenance events, increases the maintenance cost, and also increases the down time of the rig.
Accordingly, it would be desirable to provide systems and methods that avoid the afore-described problems and drawbacks.